A large number of electronic devices are mounted in a vehicle. In connecting these electronic devices and a control ECU which performs a control of these electronic devices respectively, there exists a drawback that a weight of a wire harness is increased. To cope with such a drawback, there has been proposed a vehicle-mounted system where a plurality of electronic devices are divided into a plurality of electronic units, one power source line and one signal line pulled out from the control ECU are connected to the plurality of electronic units in a branched manner, and a function of communicating with the control ECU is imparted to connection connectors connected between the power source line and signal line with the electronic units.
However, in the above-mentioned vehicle-mounted system, there exists a drawback that all electronic devices cannot be driven when an abnormality occurs in the power source line.